The present invention relates to a two phase or composite material using a first metallic material as a matrix material and with fine particles made of a second metal dispersed therein as reinforcing material, and to a method of making such a composite material.
It has been recognized in the past that it is possible to supplement various deficiencies of a first type of metallic material without deteriorating its good characteristics by dispersing particles of a second harder type of metal or of a ceramic compound (which is typically very hard) within the first metallic material. Therefore, in the prior art, in the case of light metals such as aluminum alloy, magnesium alloy, and titanium alloy, it has been attempted to increase their strength and their heat resistance by dispersing in them ceramic particles such as silicon carbide and silicon nitride and also particles of hard metals; and in the case of copper alloys such as those for making electrode tips for spot welding and for making bearings it has been attempted to increase their wear resistance by dispersing in them ceramic particles and hard metal particles to such an extent as will not substantially deteriorate their electrical conductivity and their performance as bearing materials. In the case of such a composite material including a metallic material as a matrix material and dispersed particles of metal or ceramic compound as reinforcing material, in order to effectively supplement the deficiencies of the metallic matrix material without deteriorating its useful properties the particles to be mixed must be minute and must be uniformly dispersed in said metallic material; and further, in order to make the resulting particle dispersion composite material economically, the mixed in particles must be economically available.
However, in the prior art such metal-metal particle dispersion composite materials have been made by utilizing reinforcing particles with diameters in the range of from one micron to tens of microns, which have been formed by mechanical breaking methods or atomization methods. Also, the method typically used for dispersing these metal reinforcing particles in the molten matrix metal has been either simply to mix them mechanically, or alternatively to utilize the so called jet dispersal method in which a jet of inert gas such as argon gas carrying the metallic reinforcing particles mixed with is introduced into the molten matrix metal. However, metallic particles with an average diameter of less than one micron cannot be economically produced by such mechanical breaking methods or atomization methods, and, since the metallic particles made as described above have small surface activity and have relatively poor wettability with respect to the molten metallic matrix material, the problem arises that unevenness in the distribution in the vertical direction of the metallic particles inevitably tends to occur between higher and lower strata of the molten composite material, due to the difference in specific gravities between the metallic particles and the matrix metal. In other words, it is very difficult or impossible to evenly distribute such fine metallic reinforcing particles in the molten matrix metal by mechanical mixing or by the jet dispersal method.